A rail joint assembly connects adjacent rail sections together by mechanically splicing the rail ends. Prior art joint assemblies typically involve joint bars placed along the rails across the joint, on either side of the webs and secured by glue and/or bolts. A separator such as an end post, a gasket or other spacer may be placed between the rail ends. Reinforcing fiberglass cloth may be placed into the bond line between the rail ends and between the joint bar and rail to strengthen and insulate the joint.
Some applications require electrical insulation through the rail joint, such as for signaling, track movement or train location purposes. In those applications, insulating materials are used as separators between the rail ends, and may be also used to separate the joint bars from the rails.
One typical rail joint assembly is described in U.S. Pat. No. 3,100,080 to Fiechter which discloses a fishplate bonded to either side of a rail web, with a through-bolt securing the entire arrangement. The rail is supported on a tie, with a tie plate between the tie and the base of the rail. U.S. Pat. No. 3,381,892 to Eisses discloses another typical insulating rail joint assembly configuration, having a fishplate on either side of a rail web, with an insulating paste between the web and each fishplate.
The prior art arrangement gives rise to certain difficulties. Downward forces from passing trains deflect the rail, and tend to cause greater deflection at the weaker part of the rail, namely the joint. Glue at the bond lines of the joint creates a weak point, which is susceptible to cracking and failure.
The bond lines are also weak under thermal loads. As the ambient temperature changes, the rails contract and expand, creating a shear force along the bond lines, which in turn causes joint slip and failure.
Failure of the separator between the rail ends will decrease the insulating properties of the joint, leading to possible short circuits along the track. In addition, shorts between the joint bar and the rail can occur if the glue and insulating material between those pieces fails under repeated deflections. Bar-to-rail shorts are also a concern if uninsulated metal fasteners are inserted through bars and the rail web to hold the bars in place, or if the insulating means fail. Finally, in order to reduce wear on the joint, the joint preferably lies directly above a tie, preventing excess downward deflection under the weight of passing trains. However, while locating the joint over a tie helps support the joint, electrical shorts may be caused when the joint comes in contact with a typical steel tie plate.
As noted above, another concern is the failure of a rail joint along the bond line between the rail web and the joint bars. It is known to add a layer of fiberglass reinforcing material in the bond line to strengthen the joint. The inserted material may take the form of a fiberglass cloth, as disclosed in U.S. Pat. No. 4,466,570 to Howard. However, the addition of another layer at the bond line often simply provides another plane along which the joint can fail. For example, U.S. Pat. No. 5,503,331 to Urmson Jr. et al. discloses adding a layer of fiberglass matting material in a layer of adhesive bonding material, then adding more adhesive to strengthen the joint. Urmson Jr. recognizes that the adhesive layer is often compressed too much when the joint bars are tightened around the rail web, which tends to crush the matting and squeeze much of the adhesive out of the joint, thereby weakening the bond and adversely affecting the insulating properties. Urmson Jr. therefore discloses the use of embedded non-conductive spacers in the adhesive layer, which prevent such overcompression. Another means to strengthen the joint and provide insulation along the bond line may be a reinforcing plate, as disclosed in U.S. Pat. No. 4,630,772 to Watanabe et al.
The use of through-bolts or other fasteners to secure the joint bars in place on the rail webs may cause another weakness in the joint, namely the potential for failures and stresses around the holes through the rail web. Standard rail webs tend to be fairly narrow, compared to the size of the head of the rail or, often, the thickness of the joint bars, as can be seen in the figures of any of the prior art referred to herein. This means that stresses tend to concentrate around the holes through the narrow rail web, leading to cracks and other imperfections, followed by failure of the rail web. Failure of the rail through cracking and failure of the web around a bolt hole is often a problem.
The rail web is not the only component which may be prone to failure under repeated stress. The fasteners which hold the joint bars in place on the rail webs are also subject to stresses and may fail. In particular, it is known to provide some sort of electrical insulation about the head and shaft of the fastener in an insulated rail joint assembly, thereby insulating the metal fastener from the rail and from the joint bar. For example, U.S. Pat. No. 4,466,570 to Howard discloses insulating bushing around the through bolts, as does U.S. Pat. No. 4,773,590 to Dash et al. However, neither of these patents discloses a mechanism to protect these bushings from failure, or to ensure that the bolt is still insulated from the rail and joint bars should the bushing fail during use.
As noted above, while it may be preferable to fully support the rail joint with a cross tie, this arrangement can cause difficulties in that a metal tie plate or a steel cross tie may electrically short circuit with the rail. One method to overcome the problem with a steel tie is disclosed in U.S. Pat. No. 5,918,806 to Keightley et al. Keightley discloses a tie transversely cut into elongated members, wherein the members are then rejoined end to end with insulating material between the ends. However, this method is relatively complex and expensive, as the specially manufactured ties must be placed at the correct positions during the track laying process.
Another option to decrease the chances of rail-to-tie plate shorts is through the use of an insulator between the rail and the tie plate or of an insulating tie plate. U.S. Pat. No. 4,061,270 to Wandrisco discloses an insulating saddle to electrically insulate a steel tie from the rail and from any retaining elements used to hold the rail and saddle in place on the tie. However, the tie again is specially formed to include several detents to hold the saddle and other elements in place. LBFoster Rail Products advertises insulating tie plates made of solid polyurethane and of steel coated with polyurethane. Seneca Railroad and Mining, Inc. offers a polyurethane insulating tie plate, as well as a tie plate in a rubber/fiber combination. U.S. patent application Ser. No. 10/688,206 to Urmson Jr. also discloses a specially formed insulating tie plate.
It is therefore an object of the invention to provide an insulating rail joint assembly with an increased strength and deflection resistance at the joint, where it is most needed, without unduly increasing the overall size and weight of the joint bars.
It is a further object of the invention to provide an insulating rail joint assembly with improved strength and simple construction.
It is another object of the invention to provide an insulated rail joint assembly with a strong, cohesive bond line which is less prone to failure.
It is an object of the present invention to provide an improved insulated rail joint that overcomes the foregoing disadvantages and limitations.
These and other objects of the invention will be appreciated by reference to the summary of the invention and to the detailed description of the preferred embodiment that follow.